Abstract
Inaccurate modelling of the near-surface layers of solar models causes a systematic difference between modelled and observed solar mode frequencies. This difference---known as the "surface effect" or "surface term"---presumably also exists in other solar-like oscillators and must somehow be corrected to accurately relate mode frequencies to stellar model parameters. After briefly describing the various potential causes of surface effects, I will review recent progress along two different lines. First, various methods have been proposed for removing the surface effect from the mode frequencies and thereby fitting stellar models without the disproportionate influence of the inaccurate near-surface layers. Second, three-dimensional radiation hydrodynamics simulations are now being used to replace the near-surface layers of stellar models across a range of spectral types, leading to predictions of how some components of the surface effect vary between stars. Finally, I shall briefly discuss the future of the problem in terms of both modelling and observation.
Highlights
The era of space-based asteroseismology, driven by COROT [1] and Kepler [2], has provided observations of hundreds of cool main-sequence stars in which dozens of individual mode frequencies can be measured
Various methods have been proposed for removing the surface effect from the mode frequencies and thereby fitting stellar models without the disproportionate influence of the inaccurate near-surface layers
Three-dimensional radiation hydrodynamics simulations are being used to replace the near-surface layers of stellar models across a range of spectral types, leading to predictions of how some components of the surface effect vary between stars
Summary
The era of space-based asteroseismology, driven by COROT [1] and Kepler [2], has provided observations of hundreds of cool main-sequence stars in which dozens of individual mode frequencies can be measured. To exploit this data, we need to correct for a systematic difference between observed and modelled mode frequencies caused by improper modelling of the near-surface layers of these stars: the so-called surface term or surface effect. Several authors have proposed parametrizations of the surface effect (as a function of frequency) to suppress its influence when fitting stellar models to observed mode frequencies (Sec. 3). I apologize to anyone who feels their contribution has been omitted and seek to assure them that the cause is only brevity, not malice!
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